Wet scrubbing gas contaminants of hot gases first requires quenching to reduce gas temperature which is generally accomplished as a separate step prior to introduction of the gas into scrubbing apparatus. "Quenching" means bringing hot gases into thermal equilibrium with fresh water or a quench liquid. Quenching cools hot gases from temperatures above about 750.degree. F., for example, temperatures of 1400.degree.-3000.degree. F., to temperatures of 90.degree.-200.degree. F. The exact quenched gas temperature depends mainly upon the temperature and water content of the hot gas. The quench, or quencher, is the apparatus into which hot/dry gas generated in an incinerator, for example, enters, where the gas is cooled through evaporation of water from quench liquid, and from which the gas exits in a state of thermal equilibrium with the quench liquid. The quench requires special metallurgy and careful attention to mechanical construction in all areas in contact with, or in potential contact with, hot/dry gas and with quench liquid. Quench areas that are always in contact with quench liquid can be fabricated from fiberglass reinforced plastics (FRP) or other polymeric materials. The quench must be designed and operated for maximum reliability in order to protect temperature-sensitive downstream equipment such as equipment fabricated of fiberglass reinforced plastics (FRP) or other polymeric materials. In an incineration process, for example, an incineration process in which acidic gaseous contaminants are formed, the quench experiences some of the most severe corrosion problems of the whole incineration system. The hot acidic flue gases resulting from incineration can be contained with appropriate refractory-lined carbon steel, so long as the steel is maintained at a temperature above the acid dew point. The quenched acidic gas and the quench liquid are noncorrosive to a number of FRP and other nonmetallic materials. The quenched acidic gas is also relatively noncorrosive to several special alloys.
The quench region especially subject to attack by high temperatures and also by corrosive quencher liquid is the hot-cool interface (HCI). The HCI is located at the hot gas inlet of the quencher. The HCI comprises the first zone of a quencher/scrubber or of a traditional quencher, which ends at a point where all structural parts are 100% covered with quench liquid, and thus protected from the thermal effects of the hot gas.
When properly designed, quenches operate very reliably. Direct quenching of 1500.degree. F. or hotter acidic flue gases resulting from incineration of organic materials has the additional advantage of eliminating de novo dioxin/furan formation associated with high temperatures and slow cooling of hot acidic flue gases that occur in heat recovery boilers commonly used in connection with incinerators. Since the water content of flue gas is increased during quenching, it is essential to provide a system that supplies sufficient water or quench liquid and sufficient contact between the hot flue gas and the water or quench liquid, so that the cooled flue gas is in thermal equilibrium with the quench water or quench liquid.
Following quenching, the usual procedure involves wet scrubbing of the quenched gas in a separate scrubber to remove gaseous and particulate contaminants from the quenched gas. Scrubbing systems prevent contaminants from attaining levels which may be injurious to plant and animal life and the environment. Scrubbing by the use of wet scrubbers creates large liquid-to-gas areas so that gaseous contaminants may be absorbed. The scrubbing liquid can be water, a basic solution for removing acidic gaseous contaminants, such as HCl or SO.sub.2, or an acidic solution which can be used to remove basic contaminants, such as NH.sub.3. Many types of scrubbers are available. These include venturi scrubbers, cyclonic scrubbers, spray-type cyclonic scrubbers, packed towers, and others. Many scrubbers remove particulates as well as gaseous impurities.
Although the use of a separate quencher and a separate scrubber has proved satisfactory in the past, there are certain disadvantages connected with the use of multiple pieces of equipment to first quench and then remove contaminants from flue gas and other gaseous streams commonly encountered in industrial operations. One of the disadvantages is the cost of providing and maintaining a separate piece of industrial equipment for quenching and another separate piece for removing gaseous and particulate contaminants from such gaseous streams. Another disadvantage is the necessity to control the operation of the quencher to effect optimum reduction in temperature of the gas being treated and to control the operation of the scrubber to ensure maximum removal of the gaseous and other contaminants from the gas stream.
It is therefore a principal object of the present invention to provide a system whereby flue gases and other process gas streams containing contaminants can be quenched and scrubbed simultaneously.
Another object of this invention is to provide unitary equipment for conducting quenching and scrubbing operations.
Another object of this invention is to reduce the cost of pollution control where the polluting gas stream is at an elevated temperature.
A further object of the present invention is to reduce the complexity of equipment required for quenching and scrubbing.
Yet a further object of the present invention is to improve environmental cleanup by providing an effective means for removing contaminating gases and particulates from flue gases and other hot gaseous process streams to environmentally acceptable levels.
Yet a further object is to provide an improved hot-cool interface (HCI).
Other objects and advantages of this invention will become apparent from the following detailed disclosure and description.